> I guess the /r switch allows you to do it as it doesn't modify $1. Thanks, good call. I'll check it's supported on my version of perl.

If not try this instead:

my $x = q{Here are [[a variable]] number [[of words]] in brackets};
say $x;
$x =~ s{\[\[(.*?)\]\]}{ (my $x=$1) =~ s/ /_/g; $x }ge;
say $x;

[download]

added a /g to allow multiple chunks to be processed.

Here are [[a variable]] number [[of words]] in brackets
Here are a_variable number of_words in brackets

[download]

But to improve readability I would rather opt against one-liner and call a function in the replacement part 

sub blank2under {
  my $x=shift;
  $x =~ s/ /_/g;
  return $x;
}

[download]

Cheers Rolf

update

and here a generic function to simulate /r

sub rx (&$) {
  my $c_regex=shift;
  local $_=shift;   
  $c_regex->();
  return $_
}

my $x = q{Here are [[a variable]] number [[of words]] in brackets};
print "$x\n";
$x =~ s(\[\[(.*?)\]\])( rx {s/ /_/g} $1 )ge;
print "$x\n";

[download]

In reply to Re^3: substitute characters in the RHS of a search & replace by LanX
in thread substitute characters in the RHS of a search & replace by Anonymous Monk

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